Coolant system flush and refill, what's the best procedure?

I'll be changing the water pump this weekend but after I saw the old green coolant leaking out I now know it had the wrong stuff in. I've bought Comma G40 red but I need to give it a good flush then replace. I think I'm ok with the flushing bit, I've read various advice on flushing ranging from removing the drain plug, sticking a hose in the filler and running the tap for a bit to filling with water, running the car up to temp with the heater on then draining, repeating at least five times until the water runs clear. As for refilling, again advice ranges from jacking the back up and you'll be fine to don't even both with DIY as it needs to be done with a vacuum pump?? What do the panel think? Also, what's the volume of the system and when diluting the Comma do you need deionised water or will tap water do? Thanks

Re: Coolant system flush and refill, what's the best procedu Be interested in your responses to this as I'm considering a DIY radiator change..

If I am working on the rear part coolant system I always get the car as high as possible at the rear to make sure i don't loose all the coolant and less chance of air in the system, same procedure with the front but when re-filling I always get the car as high as possible at the rear as this allows as much air as possible to escape. If I was doing a full flush I would drain everything out from the rear and have the car as high as possible at the front to aid removal and then fill with tap water, put the car on level ground and run the engine for a little while to allow the thermostat to open (although you could leave the stat out for the time being to speed the process up) and let the existing coolant dilute with the water then drain again. I would probably only repeat this three times, five sounds overkill but what is coming out would need to be clear. I wouldn't take it fully up to temp, just run it for 10 minutes (without thermostat) but you would need to get it up to full temp if thermostat still fitted, you only need to dilute the old stuff down. Once ready for the final fill, 50/50 coolant/de-ionised water never use tap water. You can buy de-ionised water in gallon tubs in some shops and it's only a pound or two max. When bleeding the system after final fill and making sure the thermostat is fitted, back end high in the air and fill, get the engine running once almost full and keep topping up until you can no longer. Run the engine for a few days with the pin up on the expansion tank until it is constantly at max on the tank. I have read 23L is the capacity. Do you already have a LTT fitted?

The Porsche air 'burping' process (if you don't have vacuum filling kit) is to fill the engine with coolant and then start the engine with the air bleed bow lifted on the coolant tank. Keep filling whilst running it at moderate revs until no more will go in. Then put the cap on, run at ~2500 rpm until at full temp, checking that the radiator return lines are hot (in the front wheel arches). Then force both fans to run at stage two (the manual suggests using jumpers on the relays) and run for a further five mins at 2500rpm, surging to over 5000 briefly every 30 seconds or so. If the coolant level warning light comes on, deactivate the fans, stop the engine and allow to cool, then top up. Then repeat the process of running to temp, forcing the fans on, etc. Porsche are quite specific about this in the manual; so I followed it when fitting a new water pump and 'stat to both my 986 and latterly my 996, and it's worked a treat - the coolant level remains rock steady and there's never any issues.

Thanks both, that's a great help, doesn't sound too daunting now. No LTT afaik (had to look that up though!)

Re: Coolant system flush and refill, what's the best procedu I replaced all three radiators on my turbo a few months ago. It was a very simple DIY. As for filling up after you drain the system follow the above recommendations to do with raising the rear of the car and applying slight revs. The slight revs are needed do potentially prevent any air pockets forming around the engine block which would lead to hot spots. The only thing I did differently was to prefill the new radiators with coolant that way there was less coolant to top up once I started the car and it warmed up. Good Luck :thumbs:

Fit an LTT whilst you are doing the pump and have the system drained, essential mod for a 3.6.

Read up on the LTT now, lots of info about Hartech but can't see a listing on there site, is this the same one or is there's have extra bells on? http://www.design911.co.uk/fu/prod7...orsche-986-Boxster---996---987-Boxster---997/

Yes, although you can get it without the housing but if you get the housing it saves fitting the LTT into it, which isn't particularly hard to do.

One thing I would say, is it is worth investing in a vacuum filling kit if you have a compressor. It amazed me how little I was able to put back in to the system without one previously. With the vac, it is so much simpler!

I used one when I changed my radiators and fitted an LTT. Pretty easy. MC

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Thank you , this is very useful, I note best to lift the rear of the car too.

I tried the tips here re jacking up the car quite high on axle stands, topping up etc. The radiators are cold at the bottom after a 20 min run so I've obviously still got a air pocket, any further tips? Best wishes Edward

I purchased two new rads and hoses not that long ago, its the second time I’ve used the vacuum system, quick and easy with no air locks.